Hitherto, there has been practically employed, as a sealing material for integrated circuits or a similar material, a heat-resistant resin (e.g., epoxy resin) to which an insulating ceramic material (e.g., silica) in microparticle form has been charged. In a trend for enhancement of integration density and capacity, developments have been carried out for producing an insulating material which exhibits low dielectric loss, particularly in a high-frequency region, in order to reduce signal loss in integrated circuits. One promising dielectric ceramic material for use in a microwave region is forsterite (magnesium silicate: Mg2SiO4), by virtue of its small dielectric loss in a high-frequency region and high insulating performance.
Regarding forsterite, there has been disclosed a method for producing an MgO—SiO2 oxide powder, which method includes mixing and crushing Mg(OH)2 powder or MgO powder with an SiO2 powder having a mean primary particle size of 10 μm or less in water; spray-drying the mixture by means of a spray-dryer; firing the mixture at 1,100° C.; and subjecting the mixture to wet-crushing and spray-drying, to thereby yield an MgO—SiO2 oxide powder having a mean primary particle size of 0.05 to 0.15 μm (see, for example, Patent Document 1). There has also been disclosed a method for producing a forsterite powder, which method includes pyrolyzing a liquid mixture at 900° C. through a spray-pyrolysis technique, wherein the liquid mixture is prepared by mixing aqueous magnesium nitrate solution and ethyl silicate solution so as to adjust the mole ratio of magnesium to silicon to 2:1 (see, for example, Patent Document 2). Further, there has been disclosed a method for producing crystalline hollow microbodies, the method including transforming a solution of an inorganic material in a hollow microbody form or a precursor thereof in a liquid medium, or a dispersion of the inorganic material or a precursor thereof in a liquid medium into a micro-drop material; and feeding the inorganic material into a high-temperature atmosphere where the microdrop-form inorganic material is sintered or melted (see, for example, Patent Document 3).
Meanwhile, there has been known a hydrophobicing surface treatment of forsterite with an agent such as silicone oil or a silane coupling agent (see, for example, Patent Document 4).